The present invention relates generally to superconductor circuits, and more specifically the invention pertains to a feed network/parallel superconductive tunnel junction circuit that acts as a doubly balanced mixer and can be utilized as a millimeter wave satellite communications link.
The present invention was developed to help demonstrate a monolithic low noise superconductive coherent receiver which could serve as a prototype for the terahertz frequency range. The essential components of the monolithic heterodyne receiver are an antenna, preamplifier, heterodyne detector consisting of the mixer and local oscillator, and an intermediate frequency (IF) or baseband amplifier.
The spectral region from 100-1000 GHz has applications for passive and active surveillance and discrimination, and secure, wideband space communications. Low atmospheric absorption bands at 94, 140, and 220 GHz provide cloud-penetrating windows for passive or active surveillance of terrestrial targets. At other frequencies, such as 120 and 180 GHz, the extremely opaque atmosphere shields from earth-based jamming of satellite-to-satellite communications. Compared to microwave-based systems, the submillimeter wavelengths offer ten to hundred-fold decrease in antenna size and system weight while improving angular resolution, key considerations for space-based systems.
Previous exploitation of this band has been nearly impossible because of a lack of device technology. Semiconductor devices, most notably gallium arsenide and waveguide-based packages degrade rapidly at short wavelengths. Superconductive devices have shown potential for high frequency operation, but incompatibilities in temperature, impedance, and power level have limited the use of superconductors with semiconductor equipment.
Recent years have seen very rapid progress in the field of cryoelectronics. In particular, superconductor devices, with their high speed and low power dissipation, have come to show great promise as future digital devices in communications links.
Prior art superconductive mixers have been single ended, with signal and local oscillator power externally combined and sent to waveguide - mounted mixer diodes. At mm-wave frequencies (100 Ghz), mixers are often starved for local oscillator (L.O.) power, causing poor conversion efficiency. Standard "single-ended" designs intentionally waste local oscillator power by weak L.O. coupling in order to maximize signal coupling and prevent signal from corrupting the L.O. source.
The task of providing a feed network/parallel superconductive tunnel junction circuit that acts as a doubly balanced mixer, is alleviated, to some extent, by the systems disclosed in the following U.S. Patents, the disclosures of which are incorporated herein by reference:
U.S. Pat. No. 3,350,649 issued to Blaeser; PA1 U.S. Pat. No. 3,621,400 issued to Paciorek; PA1 U.S. Pat. No. 4,298,990 Issued to Bielska-Lewandowska; PA1 U.S. Pat. No. 4,325,144 issued to Slusky et al; PA1 U.S. Pat. No. 4,344,052 issued to Davidson; PA1 U.S. Pat. No. 4,731,875 Issued to Mizukami et al; PA1 U.S. Pat. No. 4,749,888 issued to Sakai et al; PA1 U.S. Pat. No. 4,896,374 issued to Waugh et al; and PA1 U.S. Pat. No. 4,955,085 issued to Woody.
Blaeser discloses a frequency converter utilizing a microstrip line and a tunnel diode. The type of tunnel diode is not disclosed.
Paciorek discloses an ac signal-combining apparatus, wherein a plurality of 3 db couplers interconnect two signal sources to a signal utilization device. Several examples of mixers and modulators are disclosed.
Bielska-Lewandowska et al disclose a frequency converter in the mm and sub-mm wavelength range utilizing Josephson junctions of either a superconducting bridge type or a tunneling type.
Slusky et al discloses a hysteretic SIS junction mixer wherein the hysteretic nature of the junction allows the mixer to operate in a switching mode, thereby producing low-noise mixing with gain.
Davidson discloses a distributed array of Josephson devices having coherence. The Josephson devices can be point contacts, micro bridges, weak links, and tunnel junctions. When utilized as a tunnel junction J2, J3 and J4, they comprise two electrodes separated by a thin tunnel barrier. It is constructed as an SIS device wherein the ground plane has a layer of electrical insulation located thereover. On this is deposited a superconductor which is one electrode. The other electrode is the superconductor layer. A thin tunnel barrier is formed between the electrodes of each of the tunnel diodes J2-J4.
Mizukami et al disclose a frequency converter used for a receiver which receives signals in the UHF bank or a microwave band. It includes two mixer circuits and a hybrid coupler. At least two embodiments are disclosed.
Sakai et al disclose a Josephson transmission line device consisting of a pair of two superconducting layers and a junction layer disposed between the supercondcuting layers (SIS type). A number of preferred embodiments are disclosed.
Waugh et al disclose a broadband monolithic balanced mixer apparatus employing a unidirectional active 180 degree hybrid. Matching networks are used at all four ports of the active hybrid to achieve the desired match over the desired frequency ranges.
Woody discloses a series RF/Parallel IF mixer array utilizing SIS tunnelling junction mixer elements in heterodyne receivers such as used in radio astronomy.
The above-cited references are indicative of the ongoing need to improve superconductive mixer circuits conversion efficiency and signal coupling properties. The present invention is intended to satisfy that need.